Method and apparatus for constructing impervious underground walls

ABSTRACT

A method for constructing an impervious underground wall by continuously enlarging an excavation by dislodging and fragmenting earth material to form a trench of long length and narrow width in the ground, adding a slurry to the excavation and mixing the fragmented earth material with the slurry in situ. The method comprises the steps of providing a movable but rigid barrier member within an initial slurry filled starter hole or trench so that fluid columns of the slurry are formed on the front and rear sides of the barrier; placing an earth-cutting tool in the front fluid column in contact with the face of the starter hole opposite the front side of the barrier member; manipulating the earth-cutting tool so as to remove progressively thin layers of material from the advancing face of the trench mixing the excavated material with the slurry of the front fluid column; adding additional fresh slurry; and causing the fluid mixture of slurry and cuttings to circulate to the rear column as the barrier-cutting tool continuously advances through the ground. The apparatus includes the barrier member which is operable to remain in a substantially vertical position, or at a constant inclination, as it moves along the trench being formed. Means are provided for preventing any substantial flow of fluid from the rear to the front column except below the bottom of the barrier. The cutting tool which may be directly connected to the movable barrier member is adapted to continuously remove relatively thin layers of earth material from the end face, which material is thoroughly mixed with slurry before it is circulated to the rear column where it gradually solidifies to form the impermeable wall. Other components of the apparatus include means to raise and lower and guide the upper end of the movable barrier member and manipulate the cutting tool, means to push the combined barrier-cutter tool forward against the advancing face of the excavation and means to add additional slurry. A wall constructed according to the method comprises a continuous narrow impermeable underground structure comprised of the solidified mixture of slurry and natural soil material having no joints, breaks, connections or overlaps. Depending on the character of the slurry used in the process the final product may be either a flexible and plastic wall of mixed soil and bentonite or a rigid and strong wall of soil-cement concrete.

r [54] METHOD AND APPARATUS FOR CON STRUCTIN G IMPERVIOUS UNDERGROUND WALLS [72] Inventor: James L. Sherard, 70 Hillcrest Road,

Berkeley, Calif. 94705 [22] Filed: Nov. 4, 1970 [21] Appl.No.: 86,979 I Related US. Application Data [63] Continuation of Ser. No. 739,805, June 25, 1968,

abandoned.

52 U.S.Cl. ..6l/35,6l/63 [51] Int.Cl ..E02d5/l8 [58] FieldofSearch ..6l/35,36,39,53.64,53.62, 61/53.52, 63

[56] References Cited UNITED STATES PATENTS 2,045,112 6/1936 Upson ..61/39 2,757,514 8/1956 Wyatt .61/31 3,023,585 3/1962 Liver.... 61/36 3,310,952 3/1967 Veder... 61/35 3,326,003 6/1967 Marconi ..6l/35 3,391,544 7/1968 Daczko 6l/53.64

3,416,322 12/1968 Bodine ..61/35 3,429,126 2/1969 Wey 61/35 Primary Examiner-David J. Williamowsky Assistant Examiner-Philip C. Kannan Att0mey-0wen, Wickersham & Erickson [57] ABSTRACT A method for constructing an impervious underground wall by continuously enlarging an excavation by dislodgingand fragmenting earth material to form a trench of long length and narrow width in the ground, adding a slurry to the excavation and mixing the fragmented earth material with the slurry in situ.'The method comprises the steps of providing a movable i but rigid barrier member within an initial slurry filled starterhole or trench so that fluid columns of the slurry are formed, on the front and rear sides of the barrier; placing an earthcutting tool in the front fluid column in contact with the face of the starter hole opposite the front side of the barrier member; manipulating the earth-cutting tool so as to remove progressively thin layers of material from the advancing face of the trench mixing the excavated material with the slurry of a the front fluid column; adding additional fresh slurry; and causing the fluid mixture of slurry and cuttings to circulate to the rear column as the barrier-cutting tool continuously advances through the ground. The apparatus includes the barrier member which is operable to remain in a substantially vertical position, or at a constant inclination, as it moves along the trench being formedv Means are provided for preventing any substantial flow of fluid from the rear to the front column except below the bottom of the barrier. The cutting tool which may be directly connected to the movable barrier member is adapted to continuously remove relatively thin layers of earth material from the end face, which material is thoroughly mixed with slurry before it is circulated to the rear column where it gradually solidifies to form the impermeable wall. Other components of the apparatus include means to raise and lower and guide the upper end of the movable barrier member and manipulate the cutting tool, means to push the combined barrier-cutter tool forward against the advancing face of the excavation and means to add additional slurry. A wall constructed according to the method comprises a continuous narrow impermeable underground structure comprised of the solidified mixture of slurry and natural soil material having no joints, breaks, connections or overlaps. Depending on the characterpf the slurr used in the process the final product may be either a flexi le and plastic wall of mixed soil and ,Pamaei or ewi an leie s l-s w 999999;. a

I N VE NTOR.

JAMES L. SHERARD ATTORNEYS PATENIEDFB29 I972 sum 1 0F 5 FIG.

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INVENTDR.

JAMES L. SHERARD BY ATTORNEYS PAIENTEDFEB29 m2 SHEET 3 [IF 5 DRIVE 82 [ILII W AY m A mR W ms L S E Y A J.

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INVENTOR. JAMES L'. SHERARD ATTORNEYS METHOD AND APPARATUS FOR CONSTRUCTHNG llMlPElRVlOUS UNDERGROUND WALLS This application is a continuation of application Ser. No. 739,805 filed June th 1968, now abandoned.

This invention relates to underground walls for establishing impervious and structural barriers, particularly in soil and soft rock. More particularly, it relates to an improved slurry trench method for constructing such impervious barriers or walls in the ground and to apparatus for carrying out the method.

impervious subterranean barriers or walls are required for many civil engineering problems and particularly where it is necessary to prevent underground see page. For example, they are often required to cut ofi subterranean seepage below dams, under and through levees which hold back water bodies, and also adjacent to excavations for foundations and underground structures to prevent or reduce the flow of ground water into the excavation during construction. Impervious underground walls may also be used to control the flow of ground water for such purposes as: (1) storage of ground water for municipal or irrigation supply in underground reservoirs; (2) prevention of salt water from seeping back underground from the ocean or bays into zones of fresh ground water and contaminating it; (3) isolation of zones of contaminated ground water, such as from industrial wastes, from areas of pure ground water, etc. Where an underground barrier is required merely for preventing seepage, a flexible wall, comprised of impervious soil may be used. However, where structural strength is also required, as in basement walls for buildings, etc., such walls are comprised of concrete.

Heretofore, underground walls have been constructed by utilizing a slurry trench; that is, a trench extending below the ground level which is kept full of a slurry consisting of a mixture of colloidal mud and water. The purpose of the mud slurry, usually of sodium bentonite, is to allow the excavation to be made with vertical walls below the ground water table without the need for structural support such as bracing or sheeting. Because the mud is heavier than water, the fluid pressure in the mud in the trench is greater than the pressure of ground water adjacent to the trench. Hence, the mud tends to flow out of the trench into the pores of the adjacent ground, preventing any flow of ground water into the trench. As the mud seeps out of the trench, a thin skin of bentonite in a semisolid state, commonly called bentonitic cake," is deposited on the walls of the trench. This thin skin or cake is extremely impervious and essentially creates an impervious lining on the walls of the trench against which the pressure of the mud inside the trench acts to support the vertical trench walls during construction and before the trench is backfilled.

Prior to the present invention flexible underground walls for preventing seepage only were constructed by backfilling a previously completed trench excavation with an impervious soil which was slid down one end of the excavation. As disclosed in U.S. Pat. No. 2,757,514, the trench was kept full of mud slurry while being dug, and the soil excavated from one of its ends was processed, if desired, and then transported to the other end of the trench where it was replaced as backfill. The backfill material was then a mixture of the same soil excavated from the trench with a little bentonitic slurry proportioned to the desired consistency.

Despite a certain degree of success with the aforesaid slurry trench method, its use heretofore was limited due to several serious problems and disadvantages. For one thing, it was limited with respect to the depth of the trench attainable since the conventional draglines, backhoes, or endless conveyortype trenching machines were the only digging apparatus adaptable to the method, and these were limited in the digging depth attainable. Moreover, such machines were limited to build relatively wide trenches (6 to 8 feet) in order to attain any significant depth, which was inefficient since in many circumstances a wall with a width of two feet or less would be easily adequate to serve the desired function.

With respect to rigid underground walls having structural capabilities as well as being impervious, the practice heretofore was to fill the excavated slurry trenches with a tremied Portland cement concrete. The trenches were usually made narrower, but it was necessary to first excavate the trench in individual short length sections or panels, generally less than twenty feet in length, with especially adapted drilling rigs, clamshell buckets, or combinations thereof and then filling each section with concrete. Thereafter the sections were connected in some manner. A more detailed description of the aforesaid panel method for underground wall construction may be found in US. Pat. Nos. 3,326,003 and 3,310,952.

Among the serious problems which arose with this panel method of concrete wall construction was that the process was extremely slow and expensive. Also, it was difficult to provide an effective and permanent seal in the joints between the panels, so that there was always a possibility of leaks at these joints.

In all cases prior to the present invention all of the soil dug to create the trench was taken out of the ground leaving the trench excavation filled with only the relatively thin and low density slurry of bentonite and water (usually 65 to 75 pounds per cubic foot) before the trench was refilled with either soil or concrete to form the wall. This procedure had several main disadvantages. In some cases the trenches caved in because the bentonitic slurry was not heavy enough to support the walls. In certain pervious and coarse soils which contained large voids, large amounts of the mud slurry sometimes rapidly flowed out of the trench into the soil formation adjacent to the trench. This wasted mud and caused caving of the walls because of loss of support requiring delays to repair the caved section and replenish the lost slurry.

Also in the prior art methods, it was necessary to keep the mud slurry reasonably clean, that is, free from sand and suspended soil particles, because it was not possible to excavate rapidly or economically unless the fluid in the trench was kept fairly light in density. This requirement necessitated wasting large quantities of contaminated mud or spending considerable effort and cost in cleaning it. Also, in previous methods it was necessary to spend a considerable effort cleaning the bottom of the trenches before filling with impervious soil or concrete. Yet another limitation of the prior art methods and apparatus was that they were only useful in making vertical walls.

The present invention provides an improved and radically different method wherein the trench is kept filled with the excavated soil which is mixed with the thin slurry to form a dense, uniform mixture of the slurry and the excavated soil, which mixture is first in a fluid state and then gradually solidifies. This method overcomes all the main disadvantages of the prior art methods discussed above. It provides a much heavier fluid mixture in the trench (generally to pounds per cubic foot) which creates much higher pressures against the vertical walls of the trench and prevents any possibility of a cave-in. Because the trench is filled with a uniform fluid mixture of mud and excavated soil, all large voids encountered in the soil are plugged, and there is no possibility that large quantities of the mud will flow out of the trench. In my invention .there is no need for cleaning the slurry. Also, in my method there is no requirement for cleaning the bottom of the trench excavation.

Another important advantage of my new method is that it enables the construction of underground walls which are inclined from the vertical. This was not possible using the prior art methods and apparatus, the main reason being that in such previous methods the trench was always kept filled only with a relatively lightweight slurry of bentonite and water. Since the density of this slurry was only slightly greater than that of water, the fluid pressure exerted by the slurry to stabilize the walls of the trench was only barely sufficient in most cases to prevent caving of the walls of a vertical sides trench. For an inclined trench considerably higher stabilizing pressures are needed inside the trench to keep its one overhanging wall from caving in. Such higher pressures are not obtainable from a slurry consisting only of bentonite and water. Since in mines (HIM! the present invention, the trench is kept filled with a mixture of soil and slurry, the pressures exerted on the walls of the inclined trench are high enough to support its overhanging wall even when the mixture in the trench is still in a fluid state. Another even more important factor with my method from the standpoint of supporting the walls of an inclined trench is that only a few feet behind the advancing end of the trench the mixed soil and slurry is already in the process of changing from a heavy fluid to a plastic solid having shearing strength. Therefore, any tendency for the trench walls to cave in or squeeze together, which could only occur by compressing the plastic solid trench filling or squeezing it out of the top of the trench, is resisted by a much greater pressure than the pressure exerted by a fluid alone. Hence, a collapse of the inclined trench walls using the method of my invention is essentially impossible.

In accordance with the foregoing, one general object of the present invention is to provide an improved slurry trench method for making an impervious underground wall or barrier that overcomes the problems and disadvantages of the prior art methods, that is faster in practice and more economical in labor and materials, that facilitates the construction of either flexible or rigid, yet relatively narrow walls to depths heretofore not attainable in an economical fashion, and that allows the construction of inclined walls.

Another object of my invention is to provide a method of excavating a trench below ground in a continuous manner in which the trench is kept filled with a relatively heavy material, which is first in a fluid state and then gradually changes to a plastic solid or rigid solid state, which material consists primarily of a mixture of the particles of the soil through which the trench is excavated and a pumped-in slurry.

Still another object of the present invention is to provide a slurry trench method for constructing an impermeable ground barrier that utilizes the pressure of fluid in the trench to apply a lateral force to a movable barrier or divider member which constantly pushes a cutting tool in contact with the end face of the advancing excavation to assist in the digging process.

Another object of the present invention is to provide a slurry trench method for constructing an impermeable underground wall that utilizes a cutting tool which is usually maintained in a substantially vertical position and moves laterally against the face of the trench while progressively excavating thin slices of soil material on the face, which cuttings are allowed to drop into the fluid and to remain in and be mixed with the fluid until they are left behind as trench filling which forms the wall.

Another object of my invention is to provide a method for constructing an impermeable wall wherein a slurry mix such as bentonitic mud or Portland cement grout is mixed with natural soil in the trench and with admixtures of chemicals or soils from outside sources which may be added for the purpose of aiding in the construction or improving the final properties of the wall.

A further object of the present invention is to provide an apparatus for making a slurry trench which utilizes a movable barrier member which can be installed across the width of the trench near the end of the advancing face of the excavation in such a way that there is a column of fluid acting on both sides of the barrier, in combination with means of reducing the weight of the fluid mixture in the column on the front side of the barrier member and a cutting tool, supported and guided by the barrier which is forced against the advancing face of the trench from which it continuously removes thin layers of earth material.

Another object of the present invention is to provide an apparatus for making an impermeable wall which when operated will mix excavated material with slurry into a homogeneous blend in a trench and progressively circulate the fluid mixture rearwardly from the advancing trench face to form the wall.

Another object of my present invention is to provide a method of constructing an underground wall using slurry trench procedures in which the trench excavating and backfilling is a combined and continuous process without the individual steps of excavating the soil from the trench, leaving the trench temporarily filled with slurry alone, and refilling the trench with material to form the body of the wall by displacing the slurry with the permanent trench filling.

Another object of my present invention is to provide a method of slurry trench construction in which it is not necessary to recirculate the mud pumped in, to clean the recirculated mud or to clean the bottom of the trench before backfilling.

Another object of my present invention is to provide a method of construction of an underground trench using the slurry trench procedure in which the two hazards of caving of the trench walls during construction and of loss of slurry from the trench into the adjacent ground are essentially eliminated.

Another object of the present invention is to provide a method of construction of an underground impervious wall which is inclined from vertical.

Another object of my present invention is to provide a rigid, structural wall in the ground comprised of soil-cement concrete, which wall is continuous and free from construction joints, connections between panels or overlaps which joints and connections are sources of potential leakage.

Other objects, advantages and features of the present invention will become apparent from the following detailed description of both the method steps and the apparatus for performing the method taken in conjunction with the accompanying drawings, in which:

FIGS. 13 are schematic views in elevation and partially in section showing the initial steps of my invention for making an impermeable underground wall;

FIG. 4 is an enlarged fragmentary view in elevation and in section showing one form of apparatus embodying the principles of my invention;

FIG. 5 is an enlarged view in section taken along line 5-5 of FIG. 4;

FIG. 6 is a fragmentary view in section taken along line 6-6 of FIG. 5;

FIG. 7 is another view in elevation and in section showing the method of my invention after a portion of the impermeable wall has been completed;

FIG. 8 is a view in section taken along line 8-8 of FIG. 7;

FIG. 8a is a view in section of an inclined wall constructed according to the present invention;

FIG. 9 is a view in elevation and in section of a combined rotary type cutter and barrier member according to the present invention;

FIG. 10 is a view in section taken along line line l010 of FIG. 9;

FIG. 11 is a view in elevation and in section of another alternate form of apparatus for performing my method;

FIG. 12 is a view in section along line 12-l2 of FIG. 11;

FIG. 13 is a view in elevation showing a chisel type cutter used in combination with a movable barrier member in accordance with the present invention;

FIG. 14 is a view taken along line 14-l4 of FIG. 13;

FIG. 15 is a view in elevation and in section of another form of trench-forming apparatus according to my invention comprising a combined barrier and jet cutter;

FIG. 16 is a view in section taken along line 16-16 of FIG. 15;

FIG. 17 is a schematic view in elevation and in section showing an alternate method for creating the movable force on the barrier cutter and fluid circulation according to my invention; and

FIG. 18 is a view taken along line 18-18 in FIG. 17.

While the drawings illustrate the various steps of my method for forming an impermeable wall and also certain embodiments of apparatus for carrying out the method, it is to be understood that these illustrations are not intended to limit the invention but are presented merely to illustrate its application in the forms shown.

Throughout this specification and the appended claims it is to be understood that the term excavation with reference to the formation of the trench refers to the cutting, loosening, or fragmentation of the ground soil in digging the trench as part of the wall construction method according to my invention and should not be construed to mean that soil material is removed from the ground and either returned to the ground or replaced with another material. As will become apparent, an important feature of my invention is that substantially all of the soil cuttings resulting from the formation of the trench remain in the trench and are mixed with other materials. Hence, the term trench" is used herein to denote the zone in the ground in which the soil is dislodged from its original position and mixed with slurry; that is, the zone in the ground in which the soil is manipulated when temporarily in a fluid state.

In broad terms, my method for constructing an impermeable wall comprises the steps of: (1 forming a starting borehole or otherwise providing an initial trench extending from the ground level to the desired wall depth, preferably to bedrock; (2) filling this initial hole with a slurry mix such as bentonitic mud; (3) providing a movable rigid barrier within the hole forming front and rear fluid columns of the slurry on its opposite sides; (4) providing a cutting tool in the front column in contact with the end face of the hole opposite the barrier, which cutting tool is supported and guided by the rigid barrier; (5) manipulating the earth-cutting tool so as to remove progressively in a continuous fashion thin layers of earth material from the end face of the hole or trench, which excavated soil drops into the adjacent fluid and is thoroughly mixed by the turbulent action generated in the fluid primarily by the cutters; (6) adding fresh slurry to the trench; (7) causing the total mixture to circulate to the trench behind the barrier as the barrier-cutting tool continuously advances through the ground. The aforesaid method steps will be better understood as they are explained in greater detail below together with a description of the apparatus according to my invention.

Referring to the drawings, FIGS. 1 through 8 show progressively an impermeable barrier wall 26 in the process of being constructed in accordance with the principles of my invention. To best perform its function of cutting off seepage below the ground the wall normally extends from the ground surface 22 down to a layer 24 of bedrock, or of impervious rock or soil. Although the depth of this bedrock layer may continuously vary over a wide range, my method enables the lower edge of the wall to follow its contour and to be tied firmly to it as the wall is constructed. The preliminary steps of my method may be performed with conventional construction equipment and therefore will not be shown or discussed in detail. Essentially, the first step involves the drilling or excavation of a starter hole or trench 26 from the surface of the earth to the desired depth by means of a suitable earth auger 2h or other drill (FIG. l). The second step (FIG. 2) comprises filling the hole 26 with a slurry mix 30.

As shown in FIG. 3, an elongated barrier member 32 is then inserted into the slurry-filled hole, and the construction of the impermeable wall is now ready to commence. This barrier member extends transversely between opposite sides of the starter hole or trench 26 and essentially divides the slurry therein into two fluid columns 34 and 36. The length of the barrier member is always somewhat greater than the depth of the trench being excavated so that it will always protrude above the ground. Attached to the barrier member 32 is an earth-cutting tool 38 located in the front fluid column 34 between the barrier member and the end face dil of the hole or trench.

In the apparatus embodiment for performing my method shown in FIGS. 37 the movable barrier member 32 is essentially a rigid steel beam having an T l-shaped cross section comprised of a central web 46 and flanges M. This barrier member must fit upright within the trench with sufficient snugness to I prevent any substantial flow of slurry around its sides from its rear to the forward fluid column 34, and yet it must be able to move progressively forward within the trench. To accomplish this, I may attach a sealing strip 50 of flexible material to the inside surface of each end flange, as shown in H6. 5. Each strip 50 extends rearwardly from the edge of each flange so that it will flatten against the wall of the trench as the barrier member moves along. This reduces the necessity for the flanges M to bear tightly against the trench walls to form a seal, and yet it prevents any substantial flow of fluid around the barrier from the rear to the front fluid column.

The cutting tool 3% of the apparatus embodiment of FIGS. 3-7, which is particularly adaptable for carrying out my method, comprises a plurality of bandlike cutter members 52 of hardened steel spaced apart at approximately equal intervals along the length of the barrier member 32. These cutter members 52 are bent in a generally semicircular or trapezoidal configuration and are fixed rigidly, as by welding, to one edge of each flange 48 (see FIG. 5 Each cutter has relatively sharp upper and lower cutting edges 54 so that when pressed against the trench end face 4'1) and moved up and down through a stroke greater than their distance apart on the barrier 32, a relatively thin layer of earth material is removed from the end face of the trench with each upward and downward stroke. (See FIG. 6.) The term thin layer means a thickness of soil material less than ,the trench width. However, this thickness may vary for the different embodiments of cutters disclosed herein and for different types of soil so that in some instances a thin layer" may be several inches and in others a fraction of an inch.

The energy or power needed to cut the thin layer of material off the advancing face of the trench in the embodiment of FIGS. 3-7 can be applied simply by repetitively lifting the heavy combined barrier-cutting tool and letting it drop under its own weight. In circumstances where additional energy is desired to obtain a more rapid rate of progress, supplementary digging power may be imparted to the cutting tool by the addition of a conventional vibrator 56 fastened to the top of the barrier which will vibrate the whole barrier-cutting tool member, in the upward-downward direction e.g., a fraction of an inch several hundred times a minutes). Hence, the cutting action will be caused both by the raising and lowering of the whole barrier-cutting tool several feet and by the rapidly pulsating secondary vibrations. The vibrating action has a secondary beneficial influence in the process. It assists in keeping the mixture of slurry and soil cuttings immediately adjacent to the combined barrier-cutting tool in a fluid state in the same way that internal vibrators in wet concrete are commonly used to cause the material to flow inside forms.

The earth particles 58 (FIG. 6) cut from the advancing face of the trench excavation fall into and become mixed with the slurry in the front fluid column 34. Attached to the barrier member in the apparatus embodiment of FIGS. 3-7 is an air pipe Ml and also a pipe 60 which may be conveniently fixed to and extend along the length of the barrier web 46. The air pipe 34 is connected to a compressed air source 4-2, and the other pipe 60 is connected to a source of fresh slurry. Both of these pipes extend the full length of the barrier member, with their outlets 62 and 64, respectively, being at or near its extreme lower end. In some cases, additional jets may be discharged in the fluid columns at higher elevations.

Using the apparatus embodiment of FIGS. 3-7, a small quantity of air is constantly released in the upward direction at the bottom of the front fluid column from the upturned end 62 of the air pipe 445. The air bubbles upward causing the forward fluid column to be lighter than the column of fluid on the rear of the barrier. This causes a circulatory flow of the fluid from one side of the barrier to the other. As shown by the arrows in FIG. 4 the fluid mixture of the slurry and soil cuttings located behind the barrier flows downward, then under the barrier and then upward in the forward fluid column 34. The material rising to the top of the front fluid column is caused to circulate around the barrier member 32 and back into the trench on the rear side of the barrier. The reduction in the density of the front fluid column by aeration also causes a resultant pressure on the barrier member 32 which constantly pushes it forward thereby urging the cutters 52 against the advancing face Alt) of the excavation, thereby making the digging process more effective.

As shown in FIG. '7, the upper end of the combined barrier beam 32 may be attached by a cable 66 to a suitable operating device such as a construction crane 68 for providing it with an up and down oscillatory movement. The extension of the structural barrier beam may be guided and held vertical in conventional leads 70 fixed to the crane, which may be similar to leads used for pile driving operations. Other alternate types of construction equipment can be used within the scope of the invention for guiding and for raising and lowering the combined barrier-cutter to give it the proper cutting action.

Although the combined barrier member 32 with its side cutters 52, as shown in FIGS. 3-7, provides a unique device which produces unusually efficient results in most types of soil, other forms of cutting devices may be used for progressively excavating the thin slices of material from the advancing face of the trench. For example, FIGS. 9 and show a rotary cutter 72 which may be used in combination with a barrier 32 for advancing the trench in accordance with the principles of the present invention. Here, a series of cutter heads 74 are attached to a shaft 76 which is supported in a plurality of bearings 78 connected by fixed support brackets 80 to the barricr beam flanges 4-3. The upper end of the shaft 76 is connected to a suitable drive unit 82 which rotates the cutter heads 7 -3 at the desired cutting speed depending on the type of soil being excavated. As with the earlier embodiment of FIGS. 3-7, the barrier beam here may also be oscillated through a limited vertical stroke as the cutters rotate so that a relatively thin layer of earth material removed on each stroke will be thoroughly ground up and mixed into the slurry in the front column which mixture is continuously circulated rearwardly as the trench is advanced. If desired, this rotary cutter could be in the form of a continuous flight, helical auger.

In another embodiment of my invention the thin slices of soil are progressively cut from the advancing face of the trench by a conventional rotary drill bit 84, as shown in FIGS. ill and 12. Here, a drill rod 86 is confined by a bearing 88 connected by a pair of supports 90 to the barrier beam flanges 4-8. The end of each support 9'0 has a forked fitting 9i. providing a slot which fits over a transverse plate 92 fixed to the forward edge of each flange. Thus, the rotary cutter is slidabie up and down on the barrier beam but is restrained from moving horizontally with respect to the barrier beam.

FIGS. I3 and 114 show yet another form of my apparatus comprising a chopping cutter 94 which also is used with the barrier beam 32 for excavating thin slices of scil material from the face of the advancing trench. This chisel-type cutter can be operated with conventional equipment that provides a vertical chopping action and can be designed to cut either on the downward stroke only or in both up and down directions. When suppofied from a cable 96, as shown, the cutting energy in the downward direction is supplied by gravity. However, the cutter can be double-edged and supported on the end of a rigid rod so that energy imparted from a motor-driven cam or a hammer above the ground surface provides the cutting action. The sides of the cutter are provided with slots 9'7 that fit ove. transverse flange members 92 on the forward edges of the barrier member, thereby providing guidance for the cutter during its up and down motion.

Yet another form of cutter which may be utilized with the movable barrier beam 32 in accordance with the principles of my invention comprises a downwardly extending fluid pipe 98 having a jet nozzle outlet Iflfl capable of eroding a thin slice of material from the advancing trench face 45} (see FIGS. and I6). The fluid forced through the pipe may be compressed air, mud of a combination thereof and is provided from a suitable pressure source through the nozzle which is movably supported on the barrier beam 32 by a series of supports 192. The latter are similar to those for the drill cutter of FlG. l2 and guide the jet nozzle while allowing it to move parallel to the barrier beam so that it can start at the top of the trench and work downwardly to remove the thin layer of material.

In all the embodiments of my invention described above (FIGS. 3 through 16) the principle is the same; that is, a novel piece of equipment for excavating a trench which consists of a rigid structural barrier element with attached and guided cutters. The cutters excavate progressively thin slices off the near vertical face of the advancing trench excavation. In the two embodiments of my invention shown in FIGS. 4-7 and 940, the cutters are fixed and do not move with respect to the barrier in the longitudinal direction. The cutting action is obtained by repetitively raising and lowering the combined barriercutter tool. In the three embodiments shown in FIGS. ll-l2, I3-M and 15-16, the cutters move with respect to the barrier in the longitudinal direction, and the main cutting action is attained by raising and lowering the cutters while the barrier moves primarily in a horizontal direction.

In all the apparatus embodiments the movable rigid structural barrier element serves the same two main functions. First it acts as a fluid barrier or darn within the trench which, when moved forward in the trench at a substantially constant distance behind the advancing excavation face, creates a forward moving front fluid column of approximately constant size. This forward fluid column serves as a mixing chamber for the slurry and the excavated soil cuttings and also as a conduit through which the mixture of slurry and cuttings is transported away from the advancing face of the trench excavation. The second main function of the movable barrier is to provide the rigidity and alignment needed for supporting and guiding the cutting tool and forcing it to cut the thin slices progressively along the constant inclination parallel with the barrier member.

The method according to my invention may now be described in greater detail, first describing the construction of a flexible wall, in which only a bentonite-water slurry or mud is used and in which the finally constructed wall consists of a plastic impervious mixture of natural soil cuttings and bentonite. Later, variations of my method will be described wherein the slurry pumped into the trench is largely Portland cement and water which forms a rigid structural wall.

The action of any of the aforesaid apparatus is to cut through the ground by progressive excavation of soil from the face of the advancing trench by shaving or knocking off a thin layer of it using cutting, abrasive or jetting action as the cutting tool moves upward and downward or rotates. The excavated soil falls into the front fluid column and becomes mixed with the mud, the mixing action resulting from the turbulence in the front fluid column caused by the action of the cutters and the general circulation of the fluid. While maintaining this cutting and mixing action, the fluid mixture of mud and excavated soil in the front fluid column is caused to flow upward by pumping in air at the bottom of the column, as described earlier, or by other means, as discussed below. At the same time additional fresh slurry is pumped into the bottom or lower part of the trench, usually through a pipe 60 attached to the barrier member 32, to mix with the excavated soil cuttings and in sufficient quantity to keep the mixture of mud and cuttings in a fluid and manageable state. Most of the cuttings are carried upward within the rising flow of heavy fluid which flows out of the hole on the ground surface and then runs around the sides of the movable barrier at its upper end and drops back into the rear fluid column 36 behind the barrier. Very coarse and heavy particles in the lower elevations of the trench may drop to the bottom of the forward column of fluid. These coarser particles are then caught up in the turbulent movement of fluid at the bottom of the trench. By this action and the up and down action of the cutting tool they are moved around in the bottom of the trench, thoroughly mixed with the mud, and are finally left behind in the backfill as the cutting tool progresses forward.

An alternate method for moving the fluid mixture of mud and cuttings from the front fluid column to the trench in the rear of the barrier is shown in FIGS. I7 and 13. Here the circulating fluid is pumped from the front fluid column 34 to the rear column 36 through a circulating pipe 104 which is fixed to the barrier member 32. The pumping action shown is created by pumping air or mud down a smaller pipe we, which is attached to the barrier member 32, and by discharging the pumped air or mud in the form of an upward jet wt"; in side the circulation pipe lltl t This creates an airlift or jet" pumping action which is especially suitable for pumping heavy viscous fluids containing solid particles under low heads; however, specially adapted piston or centrifugal pumps can be used as well. Pumping may be carried out a rate such that the surface level llllt) in the front fluid column is held continuously several feet lower than the fluid level ll 12 in the trench behind the barrier. This causes the forward fluid column Bid to be lighter than the column of fluid directly behind the barrier and achieves the same results as pumping air into the bottom of the front column; that is, (l) a circulatory flow as shown by the arrows in FIG. 17 and movement of the mixture of slurry and soil cuttings from the forward fluid column to the trench in the rear of the barrier; and (2) a net forward push on the barrier and cutting tool.

In the embodiment shown in FIG. 17, the flow in the portion of the front fluid column which is below the suction end 1 M of the circulation pipe M4 is upward as in the case of the embodiment shown in FIG. 4. Above the suction end of the circulation pipe, the particles of soil 58 which are cut from the advancing face ilt) of the trench excavation fall vertically downward to the fluid surface 110 and then drop through the fluid by gravity until they are sucked into the circulation pipe and pumped to the rear of the barrier. If desired, the suction end lid of the circulation pipe lltld may be located nearer the lower end of the barrier member, in which case the direction of flow in the forward fluid column is downward for substantially its entire length so that fresh slurry is added to the forward fluid column by pouring it in at the surface or by pumping it in with jets positioned at intermediate elevations to improve the mixing action.

Another alternative method for causing a circulatory flow of the fluid mixture of slurry and cuttings from the front fluid column to the trench behind the barrier, which method is especially adaptable for use in combination with the apparatus embodiment of FIG. 9, is to pump the material with rotary impellers mounted on the rotary shaft '76. The rotary cutters 7 3 themselves can be designed to act also as rotary impellers, similar to the impellers commonly used in deep well centrifugal pumps. In this way the energy applied to the rotating shaft '76 can be used for both excavating the soil from the advancing face of the excavation 4t) and for causing an upward flow in the forward fluid column.

For all of the apparatus embodiments, additional fresh slurry of bentonitic mud is pumped through the pipe 6% (FlG. :t) to the bottom of the trench in quantities needed to assure that the circulating soil-mud mixture around the tool remains fluid and manageable and to provide the mud needed to mix with the newly excavated soil. The density of the circulating mudsoil mixture is generally kept as high as practical, so that the consistency of the mixture approaches that of a wet concrete mix. This serves to deter the larger soil particles excavated from the face of the trench from settling out of the fluid column and causes even large gravels to be floated upward in the rising forward column of heavy, viscous fluid. It also prevents any possibility that the walls of the trench could cave in, and it minimizes the subsequent compression and settlement of the trench filling.

The rate at which the barrier-cutting tool advances through the ground, and the maintenance of its vertical position, is controllable by various means, which are somewhat different for each of the different apparatus embodiments. Fundamentally, for the apparatus to function it must be kept vertical, or at a constant inclination, and propelled forward so that the cutters are always in contact with and working on the advancing end face till of the trench excavation. Primarily these activitics are accomplished by confining the upper end of the barrier member in fixed guides or leads attached to a construction crane as shown in FIG. 4, or other piece of heavy equipment, which guides or lends constrain the barrier ill member to remain vertical at its upper end. A forward propelling force is obtained by pulling the guides or leads forward, by moving the crane forward along the ground surface as the barrier-cutting tool is being operated. Because of the guidance of the stiff barrier member in the leads above the ground surface and also because of the considerable weight of the barrier, which hangs vertically as a pendulum, the barriercutting tool will generally remain vertical unless it is pulled too rapidly at the top by the crane. In the circumstance where the lower portion of the cutting tool does not excavate as rapidly as the crane moves forward on the surface, the barrier member will be subjected to bending which causes the guiding mechanism to bind and/or to tilt. In this circumstance it is necessary to stop or reduce the rate of forward movement of the crane temporarily, and allow the lower portions of the cutting tool to catch up, or to increase the effectiveness of the cutters in the lower portion of the cutting tool. One direct method for increasing the effectiveness of the lower cutters is to cause unbalanced fluid pressure on the barrier member by reducing the weight of the front fluid column with respect to the weight of the fluid acting on the rear of the barrier. As discussed above this can be conveniently accomplished by pumping air into the bottom of the forward fluid column (FIG. 4) or by pumping down the level of the fluid in the front fluid column so that it is continuously below the level on the rear side of the barrier (FIG. l7 The need for reducing the weight of the forward fluid column and for the resultant forward push on the barrier member depends to a large extent on the type of cutting tool being used, the nature of the soil through which the wall is being built and the depth of the wall. Even moderate differences in the amount of air pumped into the front fluid column can have a relatively large influence on the forward acting push created on the barrier-cutter cutting tool and on the rate of digging as illustrated in the following example:

Average gross density of fluid column (with air bubbles) in front of the cutting tool Force pushing ahead when the barrier is on the bottom of the trench lb. per cu. ft.

J) 1 2 g gp qpmjz (-90)= 150.000 pounds Other adjustments controlling the rate of excavation and the vcrticality of the barrier (using the embodiment of FIGS. 3 through 7) can be made by varying: (l) the weight and relative dimensions of the barrier-cutting tool; (2) the frequency and distance with which the barrier-cutting tool is raised and lowered; (3) the nature and energy of the vibrations applied by the vibrator; (4) the amount and character of mud pumped into the ground; (5) the details of the cutters working on the advancing face of the excavation and the cross-scctional area of the forward fluid column; (6) the details of the support of the upper end of the barrier in the guide leads (FIG. 4).

As the barrier-cutting tool moves forward, it leaves behind a trench filled with a mixture of the natural soil and slurry. With time, the condition of this trench filling gradually changes from that of a viscous fluid to a plastic solid. In this process, the fluid pressures in the backflll, which are originally higher than the pressure in the adjacent ground water, gradually dissipate, some settlement occurs and the mass finally reaches a condition of equilibrium. During the period of time that the mixture in the trench is still in a fluid state mixing water leaving the trench by seeping into the soil pores of the adjacent ground leaves a thin deposit of bentonite cake on both trench walls. The combination of the stabilized backfill of mixed bentonite and natural soil and the lining of bentonite calte on the two sides of the trench renders the wall completely impervious for all practical purposes.

In the general case, there will be a larger quantity of the mixture of slurry and soil cuttings than is needed to fill the excavated trench. This is caused by the fact that we have added the volume of slurry and. the fact that the backfill material will usually be somewhat less dense than the original soil. This excess material may be bled off", using shallow surface trenches at intervals along the work, to small waste reservoirs provided for this purpose.

Chemicals may be added to the bentonite-water slurry as fluidifiers" so that the soil-slurry mixture will flow more easily during the construction activity. In rare cases the natural soil through which the trench is excavated may be wholly devoid of sand or gravel sized particles, and it may be desirable to add some coarse soil or rock particles to improve the final properties of the backfill. This material may be dropped by a continuous process into the trench just to the rear of the movable barrier from where it will be carried downward and mixed with the backfill by the downward circulatory flow.

When constructing a rigid wall having structural strength the slurry mixed with the excavated soil consists primarily of a mixture of Portland cement and water with a small admixture of bentonite. Except for the use of Portland cement in the slurry, all other procedures are the same as described above for the construction of the flexible wall. Admixtures of chemicals may be used in the slurry to improve the fluidity of the fluid mixture, the time of set of the Portland cement, and the strength of the final wall. The walls so constructed will consist of a soil-cement concrete having a compressive strength which will depend on the type of soil through which the trench is being excavated, and the amounts of water and Portland cement used.

For this rigid type of wall I have found that the slurry pumped in should be generally in the ratio by weight within the following ranges: Portland cement 50 to 60 percent; bentonite 3 to percent; and water 47 to 30 percent. Using a slurry of such proportions, the final compressive strength of the wall may be made to vary as desired between 500 and 2,500 pounds per square inch, depending on the trench soil characteristics and the quantity of slurry used. The purpose of the small admixture of bentonite is to keep the cement in a uniform suspension until it is thoroughly mixed with the soil; that is, to prevent any tendency of the larger grains of cement from settling out of the cement-water slurry.

A further attribute of my method of underground wall construction is that the circulating fluid mixture of soil cuttings and slurry emerges from the forward fluid column to the ground surface and runs around the barrier to drop in the trench in the rear. Thus, it is a simple matter to take samples from the mixture as it flows on the ground surface around the movable barrier and make laboratory tests at periodic intervals to assure that the material has the properties desired. This gives a method of checking and controlling the properties of the backfill, and the quantity and properties of the slurry being added can be varied to give the wall the final properties desired. This is a highly desirable feature of my method of constructing flexible walls, but it is even more important for the construction of rigid structural walls.

Finally, while in my method for constructing underground walls as disclosed herein the trench is always kept filled with a mixture of slurry and the fragmented soil cuttings, my novel apparatus can also be used to dig trenches by methods in which all the excavated soil is removed from the trench. The barrier, the various cutting tools, the means for urging the combined barrier-cutting tool forward and the means for causing flow in the forward fluid column to carry away the cuttings from the advancing face of the trench excavation can all be used to dig a slurry trench in which all the soil, cuttings are removed from the excavation. This can be done easily by causing the fluid mixture of slurry and cuttings which emerges on the ground surface from the forward fluid column to flow to a settling pond, or to be pumped through a screening or centrifugal separating plant. Hence, the apparatus can be used to dig a conventional slurry trench, which can then be filled with any type of backfill.

The disclosures and description herein are purely illustrative and are not intended to be in any sense limiting, For example, while the drawings and description herein have shown the barrier and cutting tool to be in a near vertical position as they move through the ground, it is not imperative that they be in this position. The principles of the invention are the same for making: (1) a vertical wall using a procedure in which the barrier-cutters work on an inclined slope; and (2) a wall which is inclined from the vertical. For this purpose it is only necessary to provide means above ground for guiding the movable barrier and cutting tool in such a way that it is held on a constant inclination as it moves through the ground. Also, though I have shown the barrier to be a single steel structural H- beam member, other types of barriers with different sections can be used within the scope of my invention.

I claim:

1. A method for constructing an underground wall free from joints, connectors, or overlaps by progressively enlarging an initial excavation by dislodging and fragmenting the natural earth material to form a trench in the ground, adding a slurry to the excavation, mixing the fragmented earth material with the slurry in situ while keeping the trench excavation filled at all times with the slurry and excavated fragments and particles of natural soil in the form of a heavy viscous fluid, causing said viscous fluid to flow vertically within the trench so that the fragments of natural soil excavated at various levels in the ground become mixed together and said heavy viscous fluid has essentially the same properties at all depths within the trench, and subsequently allowing the viscous fluid to stabilize and form the body of the underground wall.

2. A method for constructing a flexible, impervious underground wall comprising the steps of filling an initial excavation with a slurry primarily comprised of colloidal mud and water, progressively enlarging said initial excavation to form a narrow trench by dislodging particles of natural soil material from at least one face or boundary wall of the enlarging trench excavation, continuously adding fresh slurry, mixing the dislodged fragments of said natural soil material and the slurry within the trench to form a heavy viscous fluid, causing said viscous fluid to circulate and flow vertically within the trench across the boundary wall of the trench being excavated so that the fragments of natural soil encountered at various levels within the ground become mixed together with the slurry and so that the heavy viscous fluid has essentially the same properties at all elevations, and allowing the total mixture of viscous fluid to stabilize in the trench to form the body of the underground wall.

3. The method as described in claim 2 including the step of adding aggregate materials from an outside source to the circulating viscous fluid mixture as it emerges at the ground surface, for the purpose of improving the final properties of the trench filling, such aggregate being finally distributed uniformly throughout the body of the wall.

4. A method of constructing a rigid and strong impervious underground wall of soil-cement concrete comprising the steps of filling an initial excavation with a slurry consisting primarily of cement and water, progressively enlarging said initial excavation to form a narrow trench by dislodging particles of natural soil material from at least one face or boundary wall of the enlarging trench excavation continuously adding fresh cement and water slurry, mixing the dislodged fragments of said natural soil material and the slurry within the trench to form a heavy viscous fluid causing said viscous fluid to circulate and flow generally vertically within the trench for substantially its full depth in such a way that the fragments of natural soil excavated at various levels in the ground are mixed together and then moved rearwardly in the trench, and allowing the total mixture of viscous fluid to stabilize and solidify in the trench to form the body of the underground wall.

5. The method as described in claim 4 including the step of adding aggregate materials from an outside source by dropping them into said circulating viscous fluid at the ground surface for the purpose of improving the final properties of the trench filling, such aggregates being distributed uniformly throughout the body of the wall.

6. A method for constructing an underground wall comprising the steps of:

forming an initial excavation having an end face;

filling the initial excavation with a fluid slurry;

inserting into the excavation an elongated barrier member having attached thereto on its front side an earth cutter means;

locating said barrier member within the initial excavation so that fluid columns of slurry are formed on both its front and rear sides; continuously enlarging said excavation to form a trench by progressively dislodging particles or thin layers of soil material from said end face, which is thereby advanced through the ground, and letting the soil cuttings drop into and be mixed with the fluid of said front column;

continuously moving said barrier member forward as the excavation is being enlarged in such a way that the size of the column of fluid in front of the barrier member and the distance between it and the advancing end face of the excavation remain essentially constant;

continuously adding fresh slurry to the excavation to mix with the soil cuttings so that the mixture of cuttings and slurry in the front column is maintained in the form of a heavy viscous fluid;

causing the fluid mixture of slurry and soil cuttings to be moved continuously by a flowing action from the column of fluid on the front side of the barrier member to the trench on its other side, and allowing the mixture to stabilize and form the body of the wall.

7. The method of claim 6 in which the slurry added comprises primarily colloidal mud and water so that the stabilized mixture of slurry and soil cuttings forms an impervious and flexible wall in the form of a plastic, nonrigid, solid mixture of soil and colloidal mud.

8. The method of claim 6 in which the slurry added comprises primarily cement and water so that the stabilized mixture of slurry and soil cuttings forms an impervious, rigid and strong wall of soil-cement concrete.

9. The method of claim 6 including the step of adding aggregate materials from an outside source to the heavy viscous mixture of slurry and cuttings for improving the final properties of the trench filling.

ill. The method of claim 6 in which the steps of moving said barrier member forward and of causing the mixture of slurry and soil cuttings to flow from the front fluid column to the other side of the barrier are accomplished by aerating the front fluid column to reduce its weight relative to the weight of the fluid column on the rear side of the barrier.

ill. The method of claim 6 in which the fluid mixture of slurry and soil cuttings is moved continuously from the front fluid column to the rear side of the barrier by pumping.

12. The method of claim 6 wherein thin layers of earth material are removed from the advancing end face of the trench excavation by abrading the wall surface with an up and down oscillatory action of the cutter means.

B. The method of claim 6 wherein the thin layers of earth material are removed from the advancing end face of the trench excavation by the rotary action of said cutter means.

M. The method of claim 6 wherein the thin layers of earth material are removed from the advancing wall of the trench excavation by a combined up and down oscillatory and rotary action of said cutter means.

15. The method of claim 6 wherein the thin layers of earth are removed from the advancing wall of the trench by the action of a fluid jet.

H6. The method of claim 6 wherein the thin layers of earth are removed from the advancing end face of the excavation by a lineal chopping action of said cutter means substantially parallel to the longitudinal axis of said barrier member.

l7. An apparatus for constructing an impermeable underground wall, comprising:

an elongated and rigid guide and barrier means adapted for insertion into a fluid-filled trench excavation in a generally upright position thereby forming front and rear fluid columns on its opposite sides and being laterally movable within said trench;

cutter means attached to a front side of said movable guide and barrier means;

means for manipulating said cutter means while it is guided by said guide and barrier means to remove progressively relatively thin layers of earth material in the form of soil cuttings from and thereby to advance the end face of the trench excavation;

means for continuously urging the combined guide and barrier means laterally forwardly towards the end face of said trench excavation;

means for guiding the upper end of said guide and barrier means which protrude above the ground surface to help maintain it in a vertical position or at a constant desired inclination, as it moves through the ground;

means for adding fresh slurry to the trench; and

means for causing the mixture of slurry and soil cuttings to flow from the front side of the barrier means to its rear side.

18. The apparatus as described in claim 17 wherein said cutter means comprises a plurality of scraper members fixed rigidly to one side of said guide and barrier means along its length and having edges for abrading said excavation face when moved up and down, and means for moving said barrier means up and down while said cutter means engages the excavation face.

19. The apparatus as described in claim l7 including a power driven vibrator attached to the combined barrier and cutter means for vibrating the apparatus, primarily in the longitudinal direction to assist in the cutting action and to assist in keeping the dense mixture of soil cuttings and slurry on both sides of the combined barrier-cutter means in a fluid state.

20. The apparatus as described in claim 17 wherein said cutter means comprises a rotary drill, means fixed to said barrier means for supporting and guiding said drill while allowing it to move freely longitudinally along the said barrier means along an axis which is fixed at a constant distance from the longitudinal axis of said barrier means, and means for rotating said drill and moving it upwardly and downwardly.

211. The apparatus as described in claim l7 wherein said cutter means comprises a plurality of rotary cutters on a shaft, means for supporting said shaft on said barrier means, means for rotating said shaft and said cutters, and means for moving said combined barrier and cutter means up and down while said cutter means engages the excavation face.

22. The apparatus as described in claim 17 wherein said cutter means comprises a chisel head, means fixed to said bar rier means for guiding said chisel head in such a way as to allow said chisel to move freely longitudinally along the barrier means while being forced to travel along an axis parallel to the longitudinal axis of said barrier means, and means for raising and lowering said chisel head to remove a thin layer of material from said excavation face.

23. The apparatus as described in claim 17 wherein said soil cutter means comprises means producing a fluid jet and means attached to said barrier means for guiding said latter means along an axis parallel to the longitudinal axis of the barrier means.

24. The apparatus as described in claim 17 in which said means for causing a flow in said front fluid column and the means for urging said guide and barrier means forwardly within the trench comprise means for aerating said front fluid column.

25. The apparatus as described in claim 17 in which said means for causing a flow in said front fluid column and the means for urging said guide and barrier means forwardly within the trench comprise means for pumping the fluid mixture from said front fluid column.

llllil'l'i INI'M 26. The apparatus as described in claim 17 wherein the means for urging said guide and barrier member forwardly within the trench and the means for guiding its upper end above the ground surface comprises a construction crane including guide lead means engaged with said barrier member.

2'7. The apparatus as described in claim 17 wherein said barrier means comprises a steel beam member having a transverse web and flanges on the side edges of said web.

28. The apparatus as described in claim 17 including flexible sealing means fixed to and extending beyond the edges of the barrier means on both sides for controlling or preventing the flow of fluid around the barrier means from rear to front.

29. The apparatus as described in claim 17 including a pair of pipes fixed to said barrier means and extending longitudinally thereon, means supplying compressed air to one said pipe and means supplying slurry material to the other said pipe.

30. A method for constructing an underground structure comprising the steps of:

progressively enlarging an initial excavation by dislodging and fragmenting the natural earth material to form a larger excavation in the ground, adding a slurry to the enlarged excavation, mixing the fragmented earth material with the slurry in situ while keeping the excavation filled at all times with the slurry and excavated fragments and .particles of natural soil in the form of a heavy viscous fluid, causing said viscous fluid to flow vertically within the excavation so that the fragments of natural soil excavated at various levels in the ground become mixed together and said heavy viscous fluid has essentially the same properties at all depths within the excavation, and subsequently allowing the viscous fluid to stabilize and form a solidified underground body. 31. The method as described in claim 30 wherein said slurry material is a Portland cement mixture.

32. The method as described in claim 30 wherein said slurry material is bentonite mud. 

1. A method for constructing an underground wall free from joints, connectors, or overlaps by progressively enlarging an initial excavation by dislodging and fragmenting the natural earth material to form a trench in the ground, adding a slurry to the excavation, mixing the fragmented earth material with the slurry in situ while keeping the trench excavation filled at all times with The slurry and excavated fragments and particles of natural soil in the form of a heavy viscous fluid, causing said viscous fluid to flow vertically within the trench so that the fragments of natural soil excavated at various levels in the ground become mixed together and said heavy viscous fluid has essentially the same properties at all depths within the trench, and subsequently allowing the viscous fluid to stabilize and form the body of the underground wall.
 2. A method for constructing a flexible, impervious underground wall comprising the steps of filling an initial excavation with a slurry primarily comprised of colloidal mud and water, progressively enlarging said initial excavation to form a narrow trench by dislodging particles of natural soil material from at least one face or boundary wall of the enlarging trench excavation, continuously adding fresh slurry, mixing the dislodged fragments of said natural soil material and the slurry within the trench to form a heavy viscous fluid, causing said viscous fluid to circulate and flow vertically within the trench across the boundary wall of the trench being excavated so that the fragments of natural soil encountered at various levels within the ground become mixed together with the slurry and so that the heavy viscous fluid has essentially the same properties at all elevations, and allowing the total mixture of viscous fluid to stabilize in the trench to form the body of the underground wall.
 3. The method as described in claim 2 including the step of adding aggregate materials from an outside source to the circulating viscous fluid mixture as it emerges at the ground surface, for the purpose of improving the final properties of the trench filling, such aggregate being finally distributed uniformly throughout the body of the wall.
 4. A method of constructing a rigid and strong impervious underground wall of soil-cement concrete comprising the steps of filling an initial excavation with a slurry consisting primarily of cement and water, progressively enlarging said initial excavation to form a narrow trench by dislodging particles of natural soil material from at least one face or boundary wall of the enlarging trench excavation, continuously adding fresh cement and water slurry, mixing the dislodged fragments of said natural soil material and the slurry within the trench to form a heavy viscous fluid causing said viscous fluid to circulate and flow generally vertically within the trench for substantially its full depth in such a way that the fragments of natural soil excavated at various levels in the ground are mixed together and then moved rearwardly in the trench, and allowing the total mixture of viscous fluid to stabilize and solidify in the trench to form the body of the underground wall.
 5. The method as described in claim 4 including the step of adding aggregate materials from an outside source by dropping them into said circulating viscous fluid at the ground surface for the purpose of improving the final properties of the trench filling, such aggregates being distributed uniformly throughout the body of the wall.
 6. A method for constructing an underground wall comprising the steps of: forming an initial excavation having an end face; filling the initial excavation with a fluid slurry; inserting into the excavation an elongated barrier member having attached thereto on its front side an earth cutter means; locating said barrier member within the initial excavation so that fluid columns of slurry are formed on both its front and rear sides; continuously enlarging said excavation to form a trench by progressively dislodging particles or thin layers of soil material from said end face, which is thereby advanced through the ground, and letting the soil cuttings drop into and be mixed with the fluid of said front column; continuously moving said barrier member forward as the excavation is being enlarged in such a way that the size of the column of fluid in front of the Barrier member and the distance between it and the advancing end face of the excavation remain essentially constant; continuously adding fresh slurry to the excavation to mix with the soil cuttings so that the mixture of cuttings and slurry in the front column is maintained in the form of a heavy viscous fluid; causing the fluid mixture of slurry and soil cuttings to be moved continuously by a flowing action from the column of fluid on the front side of the barrier member to the trench on its other side, and allowing the mixture to stabilize and form the body of the wall.
 7. The method of claim 6 in which the slurry added comprises primarily colloidal mud and water so that the stabilized mixture of slurry and soil cuttings forms an impervious and flexible wall in the form of a plastic, nonrigid, solid mixture of soil and colloidal mud.
 8. The method of claim 6 in which the slurry added comprises primarily cement and water so that the stabilized mixture of slurry and soil cuttings forms an impervious, rigid and strong wall of soil-cement concrete.
 9. The method of claim 6 including the step of adding aggregate materials from an outside source to the heavy viscous mixture of slurry and cuttings for improving the final properties of the trench filling.
 10. The method of claim 6 in which the steps of moving said barrier member forward and of causing the mixture of slurry and soil cuttings to flow from the front fluid column to the other side of the barrier are accomplished by aerating the front fluid column to reduce its weight relative to the weight of the fluid column on the rear side of the barrier.
 11. The method of claim 6 in which the fluid mixture of slurry and soil cuttings is moved continuously from the front fluid column to the rear side of the barrier by pumping.
 12. The method of claim 6 wherein thin layers of earth material are removed from the advancing end face of the trench excavation by abrading the wall surface with an up and down oscillatory action of the cutter means.
 13. The method of claim 6 wherein the thin layers of earth material are removed from the advancing end face of the trench excavation by the rotary action of said cutter means.
 14. The method of claim 6 wherein the thin layers of earth material are removed from the advancing wall of the trench excavation by a combined up and down oscillatory and rotary action of said cutter means.
 15. The method of claim 6 wherein the thin layers of earth are removed from the advancing wall of the trench by the action of a fluid jet.
 16. The method of claim 6 wherein the thin layers of earth are removed from the advancing end face of the excavation by a lineal chopping action of said cutter means substantially parallel to the longitudinal axis of said barrier member.
 17. An apparatus for constructing an impermeable underground wall, comprising: an elongated and rigid guide and barrier means adapted for insertion into a fluid-filled trench excavation in a generally upright position thereby forming front and rear fluid columns on its opposite sides and being laterally movable within said trench; cutter means attached to a front side of said movable guide and barrier means; means for manipulating said cutter means while it is guided by said guide and barrier means to remove progressively relatively thin layers of earth material in the form of soil cuttings from and thereby to advance the end face of the trench excavation; means for continuously urging the combined guide and barrier means laterally forwardly towards the end face of said trench excavation; means for guiding the upper end of said guide and barrier means which protrude above the ground surface to help maintain it in a vertical position or at a constant desired inclination, as it moves through the ground; means for adding fresh slurry to the trench; and means for causing the mixture of slurry and soil cuttings to flow from the front side of the barrier means to its rear side. Pg,38
 18. The apparatus as described in claim 17 wherein said cutter means comprises a plurality of scraper members fixed rigidly to one side of said guide and barrier means along its length and having edges for abrading said excavation face when moved up and down, and means for moving said barrier means up and down while said cutter means engages the excavation face.
 19. The apparatus as described in claim 17 including a power driven vibrator attached to the combined barrier and cutter means for vibrating the apparatus, primarily in the longitudinal direction to assist in the cutting action and to assist in keeping the dense mixture of soil cuttings and slurry on both sides of the combined barrier-cutter means in a fluid state.
 20. The apparatus as described in claim 17 wherein said cutter means comprises a rotary drill, means fixed to said barrier means for supporting and guiding said drill while allowing it to move freely longitudinally along the said barrier means along an axis which is fixed at a constant distance from the longitudinal axis of said barrier means, and means for rotating said drill and moving it upwardly and downwardly.
 21. The apparatus as described in claim 17 wherein said cutter means comprises a plurality of rotary cutters on a shaft, means for supporting said shaft on said barrier means, means for rotating said shaft and said cutters, and means for moving said combined barrier and cutter means up and down while said cutter means engages the excavation face.
 22. The apparatus as described in claim 17 wherein said cutter means comprises a chisel head, means fixed to said barrier means for guiding said chisel head in such a way as to allow said chisel to move freely longitudinally along the barrier means while being forced to travel along an axis parallel to the longitudinal axis of said barrier means, and means for raising and lowering said chisel head to remove a thin layer of material from said excavation face.
 23. The apparatus as described in claim 17 wherein said soil cutter means comprises means producing a fluid jet and means attached to said barrier means for guiding said latter means along an axis parallel to the longitudinal axis of the barrier means.
 24. The apparatus as described in claim 17 in which said means for causing a flow in said front fluid column and the means for urging said guide and barrier means forwardly within the trench comprise means for aerating said front fluid column.
 25. The apparatus as described in claim 17 in which said means for causing a flow in said front fluid column and the means for urging said guide and barrier means forwardly within the trench comprise means for pumping the fluid mixture from said front fluid column.
 26. The apparatus as described in claim 17 wherein the means for urging said guide and barrier member forwardly within the trench and the means for guiding its upper end above the ground surface comprises a construction crane including guide lead means engaged with said barrier member.
 27. The apparatus as described in claim 17 wherein said barrier means comprises a steel beam member having a transverse web and flanges on the side edges of said web.
 28. The apparatus as described in claim 17 including flexible sealing means fixed to and extending beyond the edges of the barrier means on both sides for controlling or preventing the flow of fluid around the barrier means from rear to front.
 29. The apparatus as described in claim 17 including a pair of pipes fixed to said barrier means and extending longitudinally thereon, means supplying compressed air to one said pipe and means supplying slurry material to the other said pipe.
 30. A method for constructing an underground structure comprising the steps of: progressively enlarging an initial excavation by dislodging and fragmenting the natural earth material to form a larger excavation in the ground, adding a slurry to the enlarged excavation, mixing the fragmented earth material with the slurry in situ While keeping the excavation filled at all times with the slurry and excavated fragments and particles of natural soil in the form of a heavy viscous fluid, causing said viscous fluid to flow vertically within the excavation so that the fragments of natural soil excavated at various levels in the ground become mixed together and said heavy viscous fluid has essentially the same properties at all depths within the excavation, and subsequently allowing the viscous fluid to stabilize and form a solidified underground body.
 31. The method as described in claim 30 wherein said slurry material is a Portland cement mixture.
 32. The method as described in claim 30 wherein said slurry material is bentonite mud. 